Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. If a photolithographic process is used to form circuits, then since the depth of focus of the optical system is relatively small, the focused surface of a stepper requires a high level of flatness One of the available processes for planarizing surfaces of semiconductor wafers is a chemical mechanical polishing (CMP) conducted by a polishing apparatus in which while supplying an abrasive liquid containing abrasive particles to a polishing cloth mounted on a rotating turntable, the semiconductor wafer held by a carrier is pressed against the polishing cloth and polished thereby.
There has been proposed a polishing apparatus having a processing section such as a polishing section accommodated in a housing so that the polishing apparatus can be installed in a clean room. In this kind of apparatus, a semiconductor wafer is taken out from a wafer cassette mounting section in which a wafer cassette is mounted, transported to a polishing section and polished therein, and the polished semiconductor wafer is cleaned by a cleaning section, and then returned to the wafer cassette in the wafer cassette mounting section.
In the above conventional polishing apparatus, the wafer cassette mounting section for mounting wafer cassettes and the processing section such as a polishing section and a cleaning section are not separated from each other, but are kept in the same environment. Therefore, the cleanliness of the processing section is enhanced to prevent semiconductor wafers in the wafer cassettes, before and after being processed, from being contaminated by the processing section. As a result, the cleanliness of the processing section is required to be higher than necessary, thus increasing the operating cost of the polishing apparatus, and the cleanliness of the semiconductor wafers in the wafer cassettes depends on the cleanliness of the processing section.
In the above conventional polishing apparatus, furthermore, after a semiconductor wafer is processed, e.g., polished, cleaned, a reference position indicated by an orientation flat or a notch of the semiconductor wafer is positioned in alignment with a predetermined direction in a separate process by a dedicated machine. Therefore, it is necessary to incorporate the separate process for positioning semiconductor wafers in the semiconductor fabrication process, and the dedicated machine for positioning semiconductor wafers is required.